The present application claims priority to Japanese Application No. P10-163092 filed Jun. 11, 1998, which application is incorporated herein by reference to the extent permitted by law.
The present invention relates to a printed circuit board and a semiconductor package using the printed circuit board.
As one type of semiconductor packages, there is known a BGA (Ball Grid Array) shown in FIG. 1, in which a semiconductor element 2 is mounted on a printed circuit board 1 and an array of solder balls 3 are disposed on the opposed side of the element mounting plane, that is, on the back face of the printed circuit board 1. The semiconductor element 2 is connected to a wiring pattern (not shown) formed on the printed circuit board 1 via bonding wires 4.
While not shown, the wiring pattern, made from a conductive material such as copper, is formed on the back face of the printed circuit board 1 on which the array of solder balls 3 are to be formed, and lands are formed in the wiring pattern. Further, a pattern protective film, such as a solder resist film, is stacked on the back face of the printed circuit board 1 in such a manner that land portions are exposed from the pattern protective film.
The above-described related art structure, however, has a problem. Namely, since the pattern protective film stacked on the back face of the printed circuit board 1 gets on outer peripheral edges of the lands, the solder balls 3 formed on the lands come into contact with the pattern protective film. As a result, when heat is applied to the BGA package, thermal stress due to a difference in thermal expansion between each solder ball 3 and the pattern protective film is applied to the root portion of the solder ball 3 (joining portion of the solder ball 3 to the land) which causes cracks at the root portion of the solder ball 3.
To solve such a problem, there has been proposed a technique shown in FIGS. 2A and 2B, in which the diameter of an opening 6a of the pattern protective film 6 located at the land formation position is set to be larger than the outer shape of the land 7, to ensure a gap between the solder ball 3 formed on the land 7 and a portion of the pattern protective film 6 around the solder ball 3, thereby preventing occurrence of cracks in the solder ball 3 due to a difference in thermal expansion.
The above technique, however, has another problem. As the land 7 is separated from the pattern protective film 6, the shear strength of the solder ball 3 is formed on the land 7 becomes weak, thereby reducing the reliability at the time of mounting the BGA package on a mother board or the like.
An object of the present invention is to provide a printed circuit board capable of preventing occurrence of cracks in external connection electrode terminals (for example, solder balls) formed on lands and enhancing the shear strength of the electrode terminals, and to provide a semiconductor package using the printed circuit board.
To achieve the above object, according to the present invention, there is provided a printed circuit board including comprising: lands formed in a wiring pattern at positions corresponding to formation positions of external connection electrode terminals; a pattern protective film having openings which are opened at the formation positions of the lands wherein the diameter of each of the openings of the pattern protective film is set to be larger than the outside diameter of each of the lands, and a reinforcing pattern which extends outwardly from an outer peripheral edge of each of the lands wherein each extension end of the reinforcing pattern is covered with the pattern protective film.
In the printed circuit board having the above configuration, since the diameter of the opening formed in the pattern protective film is set to be larger than the outside diameter of the land, it is possible to ensure, upon formation of the external connection electrode terminal, such as the solder ball on the land, a gap between the external connection electrode terminal and a portion of the pattern protective film around the external connection electrode terminal. Further, since the reinforcing pattern extends outwardly from the outer peripheral edge of the land and the extension end of the reinforcing pattern is covered with the pattern protective film, it is possible, upon formation of the external connection electrode terminal on the land, to suppress the movement of the external connection electrode terminal in the shear direction.